OAuth 2.0 enables secure delegated authorization. Implementing it correctly is crucial for security. Here's how to do it right.
OAuth Flows
Authorization Code (with PKCE):
- Best for web and mobile apps
- Most secure
- Server exchanges code for tokens
Client Credentials:
- Machine-to-machine
- No user involvement
- Service accounts
Implicit (Deprecated):
- Don't use for new apps
- Tokens exposed in URL
- Replaced by Auth Code + PKCE
Resource Owner Password:
- Legacy systems only
- User credentials sent to client
- Avoid if possible
Authorization Code Flow with PKCE
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OAuth Server Implementation
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Token Validation
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Refresh Token Rotation
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Best Practices
Security:
✓ Always use PKCE
✓ Validate redirect URIs exactly
✓ Use short-lived access tokens
✓ Rotate refresh tokens
✓ Store tokens securely
Implementation:
✓ Use state parameter against CSRF
✓ Validate all inputs
✓ Log security events
✓ Rate limit token endpoints
Token Handling:
✓ Never expose tokens in URLs
✓ Use HttpOnly cookies when possible
✓ Clear tokens on logout
✓ Implement token revocation
Conclusion
OAuth 2.0 requires careful implementation. Use Authorization Code with PKCE, validate everything, rotate refresh tokens, and follow security best practices. When possible, use battle-tested libraries rather than implementing from scratch.